Partial Differentials
by Evan Glaser
Summary: In an equation with two or more variables, each unknown can be differentiated by itself to estimate its impact on the others, but the only true way to solve the equation is to solve for all four variables. YAOI! 59,38,35,89,58,39,3589
1. First Order Derivation

Disclaimer: I do not own Saiyuki. I do not have the capacity of mind to have created Saiyuki. But I am going to do unspeakable things to the characters. Bwhahahahahaha!

Author's Note: I don't think I'm that great at writing, but I don't think anyone else is going to do what the ideas in my head are. Also, for those of you who watch the anime, Hakkai will have a glass eye like in the manga rather than a slightly deformed eye like in the anime.

Partial Differentials

Chapter One: First Order Derivation

Son Goku couldn't sleep. Okay, that is an incorrect statement. Son Goku could sleep through the apocalypse and still wake up after it was all over yelling, "Harehetta!" at the top of his lungs to all of the charred and mutilated bodies. He could sleep as a hundred or more youkai descended upon him to decimate his body and tear him limb from limb and still wake up the next morning saying, "Harehetta!" again to dead and mutilated bodies, but this time, he would have been the cause of death and mutilation, not the apocalypse. In fact, in any situation a person could possibly fathom as not being sleep through-able, the end result would be the same, with Son Goku remaining firmly asleep and still waking up in the morning saying, "Harehetta!" only not necessarily to dead and mutilated bodies.

Most of the time, the bodies on the receiving end of Goku's most frequent statement were very much alive and, depending on which person, not too thrilled to hear it for the umpteenth time.

Body one belonged to Sha Gojyo, a hanyou with long hair and striking eyes, both the color of blood. If he were the first to respond, he would lazily reprimand the youth with a "baka saru" thrown in for good measure. This would cause said saru to respond with insults along the lines of "ero kappa" and such. The two would then exchange many similar insults back and forth with escalating volume until another, very irritated, voice would drown out both kappa and saru while dealing each a blow with a paper fan. Sometimes, the fan would be bypassed in favor of a few very close, but not fatal, shots from a Smith & Wesson, five round exorcism gun.

The person carrying that gun was body number two, which belonged to Genjo Sanzo, a high Buddhist priest who didn't believe in Buddhism. This man had skin so white, it made one wonder whether he had not been living in a basement his entire life. His hair was gold (Goku thought it was bright as the sun), and his droopy eyes were a deep shade of violet. It was an interesting combination, and along with his face, people sometimes thought that Sanzo was actually a woman, much to his chagrin. He became irritated easily and often, most of the time because of said saru and kappa, and was not adverse to using violence and death threats to get his way. Once he did however, it was not long before something irritated him again.

Usually when this occurred, "Maa, maa…." would come the voice of body number three, the third and final body of the rest of this ragtag bunch. This belonged to Cho Hakkai, a human turned youkai who had short black hair, one green eye, and one glass green eye hidden behind his bangs and a monocle. He had formerly ripped this eye out in his dark and murky past for reasons which will be explained later, although anyone who reads this probably already knows them. Anyway, Hakkai was the most polite and reserved member of the group, and he was not as irked by Goku's and Gojyo's antics as Sanzo was. In fact, it usually seemed as if he enjoyed the two's constant irritation of Sanzo more than anything else.

So it was, with this group of four who traveled west, a daily routine punctuated by fights with crazed youkai and ending either at an inn or camped out somewhere in the wilderness. This particular night found the group at a small inn in a small town, resting up for what the next day would bring. They had participated in a small skirmish earlier that day in the woods surrounding the town with a small and relatively harmless group of youkai. No one in the ikkou was hurt. In fact, none of them had put any serious effort into the fight to begin with and it was over with relatively quickly.

When they had reached town, they partook in dinner as usual, with Goku and Gojyo fighting over food while Sanzo grew murderous and Hakkai grew amused. Afterwards they had paired off for their rooms as usual, Sanzo with Hakkai and Gojyo with Goku, and were currently in the process of getting a good night's sleep. All, that is, except for Goku who was currently tossing and turning restlessly, much unlike his usual self who slept like the dead while snoring loudly like a lawnmower.

This did not go unnoticed by his current roommate. Gojyo normally did not have any problems getting to sleep when Goku was partaking in his regular sleeping pattern. The snoring, while loud, had become to Gojyo a white noise which he could now drift off to without a second thought. Right now, however, the room was entirely too quiet, its silence broken frequently and irregularly by Goku's constant shifting. This break in the normal pattern was clearly noted by Gojyo who was finding it that much harder to drift off. For a while, he thought that this irregularity would soon take care of itself and the saru's snores would start drifting his way. When an hour had passed, however, the kappa became too irritated and decided to get down to the bottom of the whole situation.

"Oi, saru, what gives? I'm trying to sleep here."

"I'm not making any noise, kappa, and stop calling me saru."

"That's the point, saru. You aren't making any noise. So, what gives?"

"Nothing, kappa, so go to sleep and leave me alone."

Gojyo could tell something was definitely wrong given the slight desperation he had just heard in Goku's responses, and he was slightly miffed that he had been so readily thrown off in his show of concern. For concern it was, much as he would ever hate to say it out loud, that kept him from simply ignoring the boy and trying to sleep as usual.

"Look, baka, I can't sleep with you rustling over there, so tell me what's bugging ya so we can both get back to sleep."

Goku paused for a moment before he responded. He knew Gojyo was worried about him – after two years of traveling together, he had finally picked up on the man's protectiveness and concern for him – but what was keeping him awake was far too embarrassing for him to just tell Gojyo outright. He would surely die of shame.

Noting the pause, Gojyo sat up and look across at the younger man noticing the slight frown and…was that a blush on his cheeks? Now he definitely had to find out what was eating the saru.

"What is it?" he teased, "Thinking about that girl who came on to you yesterday? Did she make you 'excited'?"

"NO!" Goku shot up and aimed a determined glare at the kappa. "I'm not a perverted kappa like you!"

"Oh, come on, saru, the red on your cheeks tells me everything. Now who's got you all hot and bothered?"

"Nobody you sex-crazed water sprite. Not all of us think about that all the time like you do."

"But you're thinking about it now," Gojyo pushed. He had to admit it was adorable the way Goku was fighting back when it was so obvious what was ailing him. He needed a little lovin' and he needed it bad.

Goku stood up in the space between their beds as if ready to jump his tormenter and beat him to death. "I am not, so just shut up!"

But unfortunately for Goku, there was a more telling sign of his thoughts that was quite apparent now that he was standing. Gojyo's eyes flashed down to the very apparent bulge in the saru's shorts, which made his lips quirk up in an amused yet surprised grin. _Damn, _he thought, _a kid his size's got a thing _that _size_? It was barely peeking out at him from behind the boxers and from under the shirt, which was ruffled just so. Tearing his eyes away from the erection for a moment, he gave Goku a quick up and down. The boy had one fist clenched by his side, the other held up threateningly, and there was a glare of death radiating from his face. Well, as much of a glare of death as the saru could muster, anyway. Gojyo never thought he looked that threatening in his human form. _Take that diadem of his head, however…_

The kappa shuddered at the sudden thought, which caused Goku to smirk in triumph as he thought he had succeeded in intimidating his aggressor.

"Ha, feeling scared, ero kappa?"

"I see nothin' scary in here, baka saru. All I see is some punk ass kid tryin' to be tougher than he is. Kinda funny if you ask me, or maybe sad; definitely not scary."

Goku was positively growling by now, and it looked as if he was getting ready to pounce. The whole situation may have been far less amusing to Gojyo, though, if it weren't for the still incredibly apparent bulge in the saru's shorts, which hadn't lessened at all, but in fact, seemed to be getting harder. _Is he getting excited by this_? the hanyou wondered. He could feel a tightness stirring in his own loins at the thought, and he wondered how far this would go if he kept pushing. He hadn't had any action for weeks now, and it was true that Goku was fairly attractive. _This could be a grand opportunity, but how to play it…_

"So, monkey, if you're not thinking about that girl, who are you thinking about that's got your panties in a twist?"

Goku was taken aback for a second, and he saw Gojyo's eyes were not focused on his face. He followed the gaze down until he saw the bit of skin creeping out of the confines of his boxers already a little wet. He gasped and immediately turned around to hide his shame, staring at the floor and willing his erection away. It would not heed him. What had started out as stray thoughts about a certain monk had become imminent excitement as he had grown more angry and flustered with his companion. Little did he know, said companion was about to drive the nail into the coffin.

"Ooh, now he's shy, eh? Well if it isn't the girl…it's probably that sorry excuse for a monk, hai? You've been starin' at him an awful lot lately."

He didn't even see the saru move. All of a sudden, another weight was on top of him pinning his arms to the bed while angry growls emitted from the mouth of his assailant. Usually he could fight back easily, but Goku was putting a lot more effort into this fight than normal, and Gojyo knew how strong he could be. He also new that no matter what intention Goku had by attacking him like this, the monkey was still fully aroused, and he found his own arousal at a peek level as well. Since he was having a hard time using his strength against the boy currently, he decided to go for broke and use the heat between them as his weapon. He thrust his hips up sharply causing his erection to grind against Goku's. He heard a strangled gasp from above and looked up to see utter shock on the boy's face. He used the momentary lapse in the offensive to switch positions on Goku with his arms now pinning the saru down by his wrists.

Goku's eyes were wide and frantic. He started shooting his gaze off in all directions trying not to look directly at the man currently on top of him, because he was afraid what he would find there. Eventually, he felt both his wrists being held together in one hand while another grabbed his chin and forced his gaze upward to stare at the now much closer face of Gojyo. His blood red eyes were burning with an eerie fire and he smirked back in amusement at the now almost panicked face of Goku.

"You wanna play with fire, saru? Well then, let's see if you like getting burned."

* * *

I was going to include the sex in this chapter, but I got wore out. Let me know if you'd like me to continue. And for those of you rabid fans, I'm sure you have a few things to say about character and dialogue, so go ahead and say them. I don't mind. 

Any flames, though, and I go DELETED!


	2. On the Horizontal Axis

Disclaimer: Again, don't own Saiyuki, but I'm still doing naughty things to the characters.

Author's Note: I'd like to apologize about the lateness of this update. I wrote the first chapter before I went home for Christmas break and as I was heading home, I totaled my car in Iowa. The next three weeks were frenzied and filled with so much distraction that I could not bring myself to write any fiction, though I did type up a few good rants at my own situation. Now that I'm back at school and settled in, I'm gonna get those creative juices flowing again. I hope you all enjoy.

Partial Differentials

Chapter 2: On the Horizontal Axis

Gojyo's face, still smirking, inched continuously closer to Goku's, his eyes falling shut in anticipation. Goku's nose was permeated by the lingering smell of smoke, and it was making him dizzy and disoriented. His first inclination was to turn his face away from the hanyou's before there was contact of any kind, but his first attempt met with strong resistance by the hand still firmly holding his chin. His second inclination was to scream, but as his senses were engulfed by the aura of the body above him, he found that his throat was quite dry and his voice was quite gone. His brain had failed to create a third inclination, so he instead shut his eyes and lips tightly and readied himself for the oncoming assault.

Gojyo noticed the increased tension in the body below him and semi-consciously hesitated. Voices in the back of his mind were questioning his current course of action, and the waves of fear and uncertainty coming from the saru only made his conscious mind more inclined to agree. His face, however, still continued to sink down, albeit much slower, until their noses finally came into a light but deepening contact. The sense of touch finally registered into Gojyo's brain and sparked a new and frightening realization of what he was doing. His eyes snapped open searchingly and were surprised to come into contact with fearful and questioning orbs.

Goku's eyes had snapped open only moments before when he felt the skin to skin contact on his nose while at the same time sensing some trepidation in the kappa's already agonizingly slow progression towards the inevitable kiss, or at least what he thought that was the inevitable. Now, it seemed the events of the past five minutes were not going to lead to the right conclusion…or the wrong conclusion…or the conclusion that was right because that's how it was supposed to happen but wrong because this was never supposed to happen between the two of them and…

The saru's confused mind could not formulate any coherent thoughts, or at least any that Goku could himself understand, which only added to his growing apprehension. His whole body was trembling by now, but he didn't know which one of the many emotions he was feeling was the cause, and still Gojyo's face hovered so closely above his, blood red eyes searching for answers to questions Goku didn't know he was asking.

Eventually, he felt the grip on his wrists lessen; the hand holding his chin withdrew also as Gojyo sat up, drawing his body away from the boy and burying his head in his hands. Goku was still breathing hard from the moment before, and his eyes never left the kappa. He wondered if he should speak or not, but he really couldn't think of anything to say. He didn't know how to alleviate the current situation. Luckily, after a moment's time, his red headed companion broke the silence instead.

"I'm….sorry," said Gojyo in a weary tone. "I didn't know what I was thinking. I….shouldn't have done that."

Had Gojyo's tone not been so depressing, Goku might have bitten back a sharp response. At the sound of the older man's voice, though, his face fell from shock and confusion to a sympathetic sadness. "It's…well…it's not okay. But….I under…no, I don't understand either. Why…why did you do that?"

"I dunno. I just got carried away I guess." Red eyes looked up to meet gold again, this time with a tinge of sorrow painted there. "I figured it'd be harmless. I didn't think you'd be so…scared."

"I wasn't scared!" came the fervent retort. "Don't think that you could scare me any day!"

"Oh, yeah? Then why were you shaking so hard, baka saru? And I know I've never seen an animal caught in Hakuryuu's headlights with eyes as wide as yours were."

"That doesn't mean nothing, ero kappa," Goku replied angrily, "I was just…confused. I didn't know what you were doing!"

"Well, then," said Gojyo with a smirk returning to his face, "maybe I'll have to teach you." With that said, his predatory look returned with full force.

Goku stammered. "Uh…um…what do you mean by that?" If his eyes were wide before, it was nothing compared to now.

Gojyo took the opportunity to re-pin the saru to his bed. "Well, you said you weren't scared at all. That means you won't mind terribly if I get a little satisfaction tonight. Don't worry, you'll enjoy it too."

Before the boy could respond, Gojyo had his tongue down his throat and his hand stroking the still prominent erection through his pants. Unlike before, when the saru had been given time to become apprehensive, the kappa didn't take any time in driving any and all thoughts out of Goku's head. His other hand ran all over the boy's body trying to find any and every sensitive spot to exploit. Dazzled and dazed as he was, the saru could do nothing but moan and arch and press into Gojyo's ministrations, his body demanding desperately for the contact and pleading for release. The more the kappa worked his hand at Goku's erection, the harder Goku thrust his hips up trying to maximize the sensation.

As the hip thrusting became frantic, Gojyo removed his hand from the saru's crotch eliciting a sob of disappointment from the poor boy underneath him. He instead moved his hand up the boy's shirt to play with his nipples, which brought Goku down a bit from the climax he had been approaching, but left him still able to grind into his boxers. Continuing his assault, the kappa finally removed his tongue from Goku's throat and began the slow climb toward his left ear. Once he got there, he started nipping and licking the outer lobe before diving in.

If Goku was loud in his sleep, it was nothing compared to the noises he was making right now. Grunts and groans spilled out of him and, every once in a while, a fevered yelp. Most of the objections he was having to this situation previously had vanished into the swirl of sensations he was experiencing. This was the first time anyone had interacted with him in a sexual manner in his life besides his own hand, of course, and he was being put through quite the ordeal by the worldly and experienced Gojyo. If he couldn't get a release soon, he felt, he might explode from the pressure emanating from his nether regions.

While he was working on Goku's ear, the 'master of love' as it were took the opportunity to inform the boy, "Remember all of this; once that poor excuse for a monk finally gets over himself and realizes he wants you (which he does), you're gonna need this stuff." He then descended down to the saru's neck and proceeded to make it turn pretty colors.

Goku, finally distracted enough by the kappa's little speech to think a bit, decided to take the opportunity for a witty retort, which he divulged in a heated moan.

"Teach me, Sensei."

* * *

Well, not to leave you all unsatisfied, but the rest of this scene will play out in the next chapter. You will also find out what our other two companions are doing as well. 

Ta ta!


End file.
